The present invention relates to magnetic alloys of manganese-aluminum-carbon (Mn-Al-C) which show wasp-waisted hysteresis loops.
The conventional alloys of Mn-Al-C were disclosed, for example, in U.S. Pat. No. 3,661,567, etc., and have been put to practical uses as permanent magnets having excellent magnetic characteristics. Their magnetization curves represent a residual magnitization 4.pi.I.sub.r (= Br) of about 3000 G, coercive force .beta.Hc of about 1500 Oe and the ratio of 4.pi.I.sub.r to the intensity of magnetization in the magnetic field of 10000 Oe, I.sub.r /I.sub.10000, of higher than 0.5, which are all high enough to give the magnetic hysteresis loops of ordinary permanent magnets.
On the other hand, the magnetic alloys of Mn-Al-C of this invention give magnetic hysteresis loops of the shape shown in the accompanying graph which is entirely different from the shape of the aforementioned magnetic hysteresis loops of permanent magnets. This is the so-called wasp-waisted magnetic hysteresis loop, being a special magnetic hysteresis loop representing low values of 4.pi.I.sub.r and I.sub.r /I.sub.10000, which shows magnetic hysteresis mainly in the first quadrant and the third quadrant. These magnetic alloys virtually have no magnetic characteristics of permanent magnets, and have quite different usages from those of permanent magnets.
The magnetic hysteresis loop called wasp-waisted type, as shown, for example, in R. M. Bozorth, "Ferromagnetism" (1961), on pages 125 and 173, is hitherto known to appear in the process of cold working of such soft magnetic materials as Permalloys, Perminvars. Its shape is like that of the hysteresis loops of ordinary soft magnetic materials deflected to the first quadrant and to the third quadrant, with the two deflected hysteresis loops being joined to each other through a narrow or nearly straight-line part. In the magnetic materials having this characteristic, as the magnetic field is increased from zero, the permeability abruptly rises in a certain magnetic field, with the intensity of magnetization approaching 4.pi.I.sub.s ; thereafter, as the magnetic field is conversely reduced, 4.pi.I initially diminishes gradually, and then, abruptly falls down, before the magnetic field reaches zero, so that a magnetic hysteresis loop may be drawn within the first quadrant. Accordingly, 4.pi.I.sub.r takes a very low value, and I.sub.r /I.sub.s also assumes a very small value. Magnetic materials which show such wasp-waisted magnetic hysteresis loops are used for current limiters by utilizing the appreciable change of permeability in varied magnetic fields, or their applications as magnetic memories based on the utilization of this magnetic hysteresis loop have been devised.